The purpose of this study is to test the antidepressant effects of orally administered melatonin in patients with winter depression. Melatonin is a hormone produced by the pineal gland and is normally secreted at night. We are able to examine the timing of the body's clock by measuring the levels of this hormone in the blood. Investigators in this experiment have obtained synthetically derived melatonin from a pharmaceutical or chemical company in the form of capsules, which will be administered orally (by mouth) during this experiment. To date, the most effective means of treating winter depression is by appropriately-timed daily bright light exposure. Bright light therapy has the disadvantage of being time-consuming and sometimes inconvenient. In this study, we will administer melatonin for the purpose of advancing (shifting to an earlier time) or delaying (shifting to a later time) the internal body clock. We think that appropriately-timed melatonin administration will reduce symptoms of winter depression. A secondary purpose of this study is to link circadian rhythms to a genetic marker. Participants may choose to not participate in the genetic portion of this protocol and still be a part of the study.